Toning and intensifying solutions



Patented May 16, 1939 TONING AND 7 2,158,184 m'rsnsmrmc soumoiws KennethC. D. Hickman and John 0. Becker,

Rochester, N. Y., assignors, by mesne assignments, to Eastman KodakCompany, Jersey City, N. .L, a corporation of New Jersey 1 No Drawing.ApplicationApril 27,1934, Serial No. 722,730. Renewed March 12, 1938 5Claims.

' This invention relates to toning and intensifying solutions fordeveloped photographic images, whether in the form of negatives orprints, and more particularly to a new type of single solution toningand intensifying bath. I

As is well known, silver salts will react with other soluble salts, butmetallic silver is attacked most readily by elementary substances ortheir equivalents. It is for this reason that one of the best knownmethods of sulfide toning involves first, the conversion of the metallicsilver to a salt, such as silver bromide, by treatment with a mixture ofpotassium bromide and potassium ferricyanide and, second, the conversionof the silver bromide to silver-sulfide by double decomposition withsodium sulfide. This particular conversion, however, cannot be made inone stage in a single solution because the ferricyanide attacks thesodium sulfide more readily than the silver. The problem is then to findan oxidizing agent sufficiently powerful to oxidize the silver and yetbe compatible with the sulfiding agent. A number of single solutionsulfide toning processes have been developed to solve this problem, buteach sufi'ers some drawback. In the well known hypo-alum process, forexample, the bath draws sulfur from the hypo and oxidizer from the air,but the solution must be heated and the process is slow. Other sulfidetoning baths comprising sodiumor barium sulfide and sodiummetanitro-benzene sulfonate are slow in action and vile in odor.

It is the principal object of the present invention to provide a singlesolution toning bath which will meet many of the requirements of suchbaths without at the same time possessing the limitations of thehitherto known solutions. A further object is to provide a singlesolution bath which may not only be used for toning the image, but alsofor intensification. A still further object is to provide a bath of thistype possessing the novel property that it may be employed for toning aphotographic image immediately after development and before fixing. Withthe above and other objects in view ,which will become apparent as thedescription proceeds, we have set forth our invention in the followingspecification and examples which are included merely for purposes ofillustration and not as a limitation thereof.

We have discovered that various thio-compounds or their derivativesnotably the soluble thiosulfates, the trithionates .andtetrathionatesmay be employed for the toning and intensification of silver images.These thio compounds, although sometimes grouped in separate classes inthechemical text books, may, for the purposes of this. invention, begrouped in one class, because they all contain available sulfur in itsdi-valent condition. Many other substances contain divalent sulfur,mostly the thioureas and the polysulfides, but in these cases thedi-valent sulfur is connected to an unlike atom or to anotherunsaturated sulfur atom. The di-valent sulfur in the class of compoundsconsidered within the scope of this invention is connected byone or twobonds to another sulfur atom, which latter atom is otherwise fullyoxygenated and is in its hexa-valent condition. We shall find itconvenient first briefly to discuss the trithionates and tetrathionatesafter which we shall discuss the thiosulfate derivatives, in particularthe compounds of thiosulfuric acid and organic substances containing aquinone or hydroquinone grouping. In these discussions we shall refer tosome of the broader theoretical aspects of our discovery, although weare not to be understood as in any way limiting our invention thereby.

We have found that the silver salts of all three classes of compoundsreadily eliminate silver sulfide and that the trithionates andtetrathionates are particularly valuable in our invention because theyare stable in the presence of acid and mild oxidizing agents. This is ofespecial importance, since in order to be suitable for use in a toningsolution, the toning agent must be of the kind which will produce asilver salt which will readily decompose into silver sulfide as fast asthe metallic silver is oxidized, as otherwise the image will wander orsuffer reduction. Although neutral permanganate orpermanganate-phosphate admixtures with the thionates form somewhatreducing baths, which are, nevertheless, quite operative for thepurposes of our invention, ferric salts, such as ferric sulfate, and theabove mentioned thionates, give conversion to sulfide with only a slightloss. Typical toning solutions produced from the thionates according toone form of our invention are given below:

(Trithionate) Water c. c Ferric sulfate g.. '1 Sulphuric acid c. c 0. 25Potassium trlthionate g 1.5 (Tetrathionate) Water c.c 100' Ferricsulfate g I 1 Sulphuric acid c. c 0. 25 Potassium tetrathionate g 1.5

(Tetrathionate) Water c.c 100 Potassium permanganate g .1 Di-scdium acidphosphate g 8.8 Potassium tetrathionate ;g 1.0

While in the above description and examples to their potassium salts, wemay employ them in the form of the sodium, rubidium, caesium, ammonium,calcium and the like compounds. In fact, almost any soluble thionate maybe employed with equal facility according to our invention.

The tones produced by the above solutions are an unattractive yellow,but the images are light sensitive and can be intensified, if desired,by treatment with solutions of double silver nitrite or sulfite, asdescribed for example in the Journal of the Franklin Institute for 1933,vol. 216, pages 59, 627, 683, and 706, the first loss on toning beingthus more than recovered.

We come now to consideration of the thiosulfates as sulfiding agents oras sources of labile sulfur. thiosulfates such as hypo will tolerate(though only for a short time) is ferricyanic acid, con-' veniently inthe form of the potassium salt. A mixture of hypo and potassiumferricyanide, as ordinarily compounded, is, however, not a sulfidingagent, but an almost perfect solvent for the silver image, constitutingin fact, the wellknown Farmers reducer This is because the silverthiosulfate first produced is dissolved by the excess thiosulfate beforeit has time to eliminate silver sulfide. We have discovered that if therelative proportions of the hypo and ferricyanide are reversed, a weaksulfide toner is produced, some of the silver in each density beingconverted to sulfide before the more usual reduction process hasoperated. Further to emphasize this important point, we give, side byside,

Such a toning bath as the right-hand one above, which is applicable tospecial processes, is not of general usefulness because of its shortlife and incomplete action. We have, however, made the fortunatediscovery that certain organic thiosulfuric acid derivatives possess atone and the same time a greater stability toward acid and oxidizingagents and a greater instability toward silver so that their silversalts, which are more easily formed, are also more easily broken up,depositing silver sulfide. Such derivatives may be employe-das tonerswith excellent results.

Among these derivatives may be mentioned the quinone and hydroquinonederivatives of thicsulfuric acid. Of the hydroquinone compounds,hydroquinone monothiosulfuric acid, hydroquinone dithiosulfuric acid andhydroquinone tetrathiosulfuric acid may all be formed by the reaction ofa thiosulfate and quinone under controlled conditions. The conditionsare not difiicult to obtain and the acids are all easily pre- I pared;the mono form resulting from dropping quinone dissolved in dilute aceticacid into ordinary hypo, the di form by adding hypo to quinone in aceticacid, while the tetra form separates in almost theoretical yield whensolutions of chromic acid and hypo are added simultaneously to asolution of quinone in acetic acid. These three hydroquinonethiosulfuric acids are One of the few oxidizing agents that consideredto have the following structural formulae:

S S 02H Hydroquinone monothiosulphuric acid Hydroquinone dithiosuliuricacid Hydroquinone tetrathiosulluric acid It will be seen that each acidcontains sulfur in the condition specified above as important to thisinvention, namely, attached to another fully Hydroquinonetetrathiosulfuric acid g .5 Quifione--- g 1.0 Sulfuric acid c .25 Waterc c' 100.00

The above bathcan be used continuously un-- til the concentration ofhydroquinone produced in the toning reaction becomes so high that anequilibrium mixture results which is non-reactive. The activity of thebath can then be restored, by adding chromic acid, although therejuvenated bath stains slightly from dyes produced by 'secondaryoxidation.

A toning bath containing as much as 1 per cent of free mineral acid mayhave a somewhat harmful effect on gelatine emulsions and films andprints to be intensified in such a bath should be fixed in hypocontaining alum and the toning solution should likewise be loaded withalum. Bearing in mind that hydroquinone is a product of the toningreaction, the toning solution in use cals which are readily available inthe photographic laboratory. Inasmuch as the toning solution does notkeep well, its constituents should be bottled separately, a convenientrecipe being as follows:

Solution A Water c. c 500 Potassium dichromate g 16 17 Sulfuric acid(c0nc.) g

Equal portions of the firstthree solutions are employed, B being pouredinto A in a thin stream with rapid stirring, after which 0 is added tothe mixture, also with stirring. The resulting solution is then cooleddown to below 70 F. for use.

If a quicker bath is needed, one tenth the volume of Solution C mayreplace Solution C. A very vigorous bath may, for example, have thefollowing formula:

- Hydroquinone dithios'ulfuric acid g .5 Quinnne 2' 1.0 Sulfuric acid g.25 Water c. 0. 100.00

This solution should be used at about -75 F.

An example of atoning bath containing hydroquinone monothiosulfuric acidhas the following composition:

Quinone g 1.0 Water c, c 100 Sulfuric acid c. c 0.25 Hydroquinonemonothiosulfuric acid (conveniently in the form of its potassium salt) g0.5

This toning solution produces a reddish-purple tone which can be variedby varying the quantity of the hydroquinone salt as desired.

While we do not wish to confine ourselves to any particular theory orexplanation of the mechanism involved in the various reactions in toningby means of these hydroquinone thiosulfuric acids, we believe that thefirst product of toning is n nt silver sulfide, but a silverhydroquinone thiosulfate, for example, silver hydroquinone dithiosulfatein the case of a solution such as indicated in the preceding paragraph.This salt is creamy white and very insoluble, but in the presence'of theexcess oxidizing agent and acid soon changes to a greenish black. Thiscompound which constitutes the toned or intensified imagewe believe tobe the silver salt of a complex dye formed by acid oxidation from thehydroquinone dithiosulfate. The reactions taking place with the mono"and "tetra" forms of the hydroquinone thiosulfuric acid are, we believe,similar I to those occurring with the di form. The first stage in allthe reactions isa. bleaching of the image by virtue of formation of thesilver salt,

being the splitting off of silver sulfide from the silver thiosulfatechain.

One of the remarkable properties of our toning baths is that they'can beadapted to tone the,

image immediately after development and before fixing. This is dueto,the fact that the solubility of the first stage toning productisijust less than ,that of thesllver halides which permits the metallicsilver to be converted to silver sulfide under conditions where silverhalide remains substantially unattacked.

Toning.-Where toning of a print or film, as

distinguished from intensification, is desired, the

print (or film) after double fixation and a tenminute wash to'assure theremoval of all soluprints, and containing 'hydroq'uinonetetrathiosulfuric acid, and rocked gently until toning is complete. andshould the vapor tend to escape, the tray can be covered with a sheet ofglass or Celluloid. The print should then be washed for about 45 minutesto remove the yellow coloration of the whites produced by the quinone.If not completely removed in this way, the yellow color may beeliminated by immersion in a 2% solution of sodium bisulfite at the endof the first ten minutes of washing. I

Intensification.-'I'he print or film to be intensified is first placedin a new unused bath containing' 10-20% of plain hypo for five minutes.It is then washed for ten minutes and placed in a bath such as describedabove and containing hydroquinone di-thiosulfuric acid, quinone, alumand acid. Two or three minutes are generally required before thereaction is well under way, but when once started can lead to anincrease in density of as much as 3'to 5 times inthe course of a halfhour. The photograph should then be washed for 10-15 minutes.

The colors of the toned image with the hydroquinone thiosulfuric acidtoners will vary from brown to a greenish black. The actual colorproduced varies with the relative quantities of reagents in the bath andwith the nature of the theless, they come within the broad scope of ourinvention, as indeed do any organic compounds containing availablesulfur attached to the molecule by another fully oxygenated sulfur atom.No

useful purpose would be served by including examples of all of thesubstituted compounds which are operative in our toning baths, but thefollowing will serve to illustrate the compositions of typical toningbaths in which various chlorb derivatives may be employed.

I. Quirione g 1.0 Water 'c. .c 100.0 Sulfuric acid c, c..- .25 andmonochlorohydroquinone monothiosulfuric acid in amount to form asaturated solution.

II. Quinonel g 1.0 Waterc. c 100.0 Sulfuric acid c c .25 anddichlorohydroquinone monothiosulfuric acid in amount to form a saturatedsolution.

III. Water c. c 100 Sulfuric acid c. c 0.25 and The bath is rich involatile quinone monochloroquinone monothiosulfuric acid in an amountsuflicient to saturate the solution.

Although in the above description we have referred mainly to toning andintensifying baths gquinone monothiosulfuric' acid and hydroquinonedithiosulfuric acid or a mixture of all three of the mono-, di-, andtetraforms.

As previously indicated, in those cases where a quinone thiosulfuricacid is employed, it is not essential to employ an oxidizing agent dueto the fact that the quinone thiosulfuric acid acts as its own oxidizingagent. With the hydroquinone thiosulfuric acids, on the other hand, itis essential to employ an oxidizing agent. Furthermore, thesethiosulfuric acids may be used, either in the form of the acid itself orin the form of a soluble salt, such as the potassium salt, it merelybeing a matter of convenience as to which form is employed.

What we claim is:

1. The process of toning and intensifying a developed silver image in aphotographic film which comprises treating said image with an aqueoussingle solution toning and intensifying bath containing as its essentialtoning and intensifying constituent a quinone. thiosulfuric acidselected from the group consisting of quinone monothiosulfuric acid,quinone dithiosulfuric acid and quinone tetrathiosulfuric acid.

2. The process of toning and intensifying a developed silver image in aphotographic film which comprises treating said image with an aqueoussingle solution toning and intensifying bath containing as its essentialtoning -and intensifying constituent quinone monothiosulfuric acid.

3. The process of toning and intensifying a developed silver image in aphotographic film which comprises treating said image with an aqueoussingle solution toning and intensifying bath containing as its essentialtoning and intensifying constituent quinone dithiosulfuric acid.

4. The process of toning and intensifying a developed silver image in aphotographic film which comprises treating said image with an aqueoussingle solution toning and intensifying bath containing as its essentialtoning and intensifying constituent quinone tetrathiosulfurio acid.

5. The process of toning and intensifying a developed silver image in aphotographic film which comprises treating said image with an aqueoussingle solution toning and intensifying

